Timed or controlled (or rather sustained) drug-delivery systems are well known in the pharmaceutical industry. However, this type of technology is not well known in the contact lens industry. This is partially due to the fact that most contact lenses are made from monomers polymerization (curing). Typically, polymerization of monomers is not very efficient; so that there remains a significant fraction of monomers after the “cure” is complete. Most of the time, these monomers could represent a serious health issue, so unpolymerized monomers are required to be extracted (i.e., removed) in an appropriate solvent extraction process using the formed contact lenses.
One problem associated with extraction is that this process is non-selective in its nature. Anything that is soluble in the employed solvent and is capable of leaching out of a formed contact lens; can (and usually will) be extracted. If there is a desired active compound or ingredient (e.g., a lubricant, a drug, etc.), all or most of the active compound or ingredient will also be removed in this extraction process, leaving a contact lens that is unable or inefficient in delivering the desired active compound or ingredient. In addition, in the extraction process, the lens is swollen so that any unbound moieties can be easily removed.
Industries have tried to overcome this problem by “loading” the polymerized article after-the-fact. This is accomplished by swelling the article in an appropriate solvent (much like in an extraction step) and then solubilizing the active compound/ingredient into that same solvent. After equilibrium, the loaded-product is removed from the solvent, allowed to dry to remove the solvent, or solvent exchanged to a solvent that does not solvate the loaded-active nor does it swell the polymer matrix; resulting in a dry-loaded article that is capable of releasing the desired compound or ingredient. However, there are several disadvantages associated with this “loading” process. First, it requires many additional steps, which can increase production costs. Second, its efficiency largely depends on the solubilization parameter of the compound or ingredient. Third, the article must be dried or solvent exchanged. In contrast, hydrogel contact lenses are stored in a packaging solution, in a hydrated state. Fourth, once the article is hydrated, the release mechanism is activated. Since hydrogel contact lenses are stored in a packaging solution, all or most (much) of the active compound or ingredient is already released in the packaging solution.
Therefore, there exist a need for methods for making hydrogel soft contact lenses capable of delivering an active compound in a sustainable manner over an extended period of time. There is also need for an ophthalmic device capable of delivering an active compound in a sustainable manner over an extended period of time.